1. Field of the Invention
This invention relates to a twisting apparatus for ultrafine rectangular bar whose cross section is formed in a rectangular shape such as a triangle or square to be formed in a spiral shape upon twisting the ultrafine rectangular bar.
2. Description of Related Art
In dental treatments, while a surface of a calcified root canal wall is cut, cutting debris or contents filled in the root canal are removed to expose a new surface of the root canal wall and to form the root canal. Endodontic devices including files and reamers having different diameter sizes are provided as instruments for forming such root canals. Some of those files and reamers are provided in having a rectangular cross-sectional shape and different diameter sizes, which are selectable according to the procedure of the treatment.
For example, a K-file is provided in having a cross section in a triangle or square shape, having a work portion formed in a spiral shape with a relatively narrow pitch made by a twisting process, and having a function to shave the root canal wall mainly upon pushing and pulling manipulations and to remove the shaved debris and contents. A reamer is provided in having a cross section in a square shape, having a work portion formed in a spiral shape with a relatively wide pitch made by a twisting process, and having a function to shave the root canal wall mainly upon rotational manipulations and to remove the shaved debris and contents.
Such K-files and reamers are standardized having diameters at a distal end of 0.02 pitch between 0.06 mm and 0.10 mm, 0.05 pitch between 0.10 mm and 0.60 mm, and 0.10 pitch at 0.60 mm or higher but up to 1.40 mm. Accordingly, the materials are formed as square bars having the same cross section as the targeted products.
The apparatus for twisting ultrafine rectangular bars having such diameters and cross-sectional shapes includes a chuck for holding the ultrafine rectangular bar as a material, and a plurality of vise clamps for restricting the ultrafine rectangular bar in contact with the side surface of the bar. After the ultrafine rectangular bar having the same cross-sectional shape and diameter as the targeted products is held by the chuck, the ultrafine rectangular bar is made in contact with the vise clamps, and then, the bar can be twisted by rotating correlatively the chuck and the vise clamps and isolating the chuck and the vise clamps from each other as restricting the ultrafine rectangular bar with the vise clamps (see, e.g., Japanese Patent Publication Nos. JB-61-53059, JB-62-22733).
With the above twisting apparatus, however, the positional relation between the corner portion of the ultrafine rectangular bar held by the chuck and the vise clamp is not controlled at all. That is, when the vise clamp is made coming closely to the ultrafine rectangular bar, what portion of the ultrafine rectangular bar comes in contact with the vise clamp is not managed. Therefore, when the twisting work for the ultrafine rectangular bar is started, the twisting starting position may be deviated in the axial direction between starting where the vise clamp contacts with a plane and starting where the vise clamp contacts with a corner portion, so that there arises a problem that the length of the twisting portion become not unified.